Separation of mineral mixtures



Oct. 16, 1951 Q L M N 1 2,571,835

SEPARATION OF MINERAL MIXTURES Filed March 21, 1946 INVENTOR JoRsEN OLAV CLEEMANN ATTORNEYS Patented Oct. 16, 1951 2,571,835 SEPARATION OF MINERAL MIXTURES Jorgen Olav Cleemann, Copenhagen, Denmark, assignor, by mesne assignments, to Separation Process Company, Catasauqua, Pa., a corporation of Delaware Application March 21, 1946, Serial No. 656,049 In Denmark March 23, 1945 1 Claim.

This invention relates to the separation of mineral materials containing components of different specific gravities into fractions made up mainly of light and heavy particles, respectively. More particularly, the invention is concerned with a novel method of separating mineral materials of the kind referred to, which is superior to prior methods in that, by its use, it is possible to treat the materials in a shorter time and,

also, to obtain a cleaner separation. The new method involves the application of the float and sink principle but utilized while the material being treated is subjected to centrifugal action, so that the separation is more eflective and the improved results mentioned are obtained.

Separation of the components of mineral mixtures, such as coal of high ash content, by use of the heat and sink principle has been carried out heretofore, and, in the practice of the prior methods, the ground mineral is mixed with a parting liquid and allowed to settle. The parting liquid is of a specific gravity which usually liesbetween those of the lightest and heaviest particles in the material to be treated and is ordinarily not a pure liquid, but, instead, is an aqueous suspension of one or more finely ground substances, such as limestone, clay, magnetic iron ore, galena, etc. When such a mixture of the ground mineral material and a parting liquid of the appropriate specific gravity is allowed to stand, the heavy particles in the material settle out while the light ones float, so that the light and heavy particles may be separated. However, the operation is relatively slow and the amount of material that may be handled per unit volume of parting liquid is small. Also, the cleanness of the separation is not wholly satisfactory.

In the method of the invention, the separation of the light and heavy particles of the mineral material is accomplished by the action of centrifugal force, the amount of which can be controlled and may be a multiple of gravity, so

' that the time required for the operation is re- 2 1y reduced to free the grains, while the fine particles eliminated are those which are unsuited for separation according to the sink and fioat principle.

The reduced mineral material to be treated is mixed with a parting liquid, which may be an aqueous suspension of one or more finely ground substances referred to above, and has a specific gravity which may lie between that of the light and heavy particles of the mineral material. In practice, it has been found possible and frequently advantageous to employ a parting liquid, the specific gravity of which is approximately the same as or even a little less than that of the light mineral particles. In some instances, it is desirable to subject the parting liquid to centrifugal separation in a preliminary operation in order to remove coarse particles, which might otherwise be precipitated with the heavy particles of the mineral material to be treated. When the parting liquid is subjected to such a preliminary separation, that operation is preferably carried on in such a way as to reduce the water content of the parting liquid. This reduction in water content serves a useful purpose to be pointed out hereafter.

The mixture of parting liquid and mineral material is fed to a centrifugal separator which may conveniently be one of the continuously operating type. While centrifugal separators of different kinds may be employed, the type best suited for the purpose is that in which the separation takes place in a rotary casing within which a spiral or similar conveying device rotates on the same axis as the casing but at a difierent rate. The conveying device advances the heavy particles along the inner wall of the casing to discharge them at one end, while the light particles leave thecasing at the opposite end. When the mixture of mineral material and parting liquid is treated in such a separator, two fractions are produced, each containing some of the parting liquid, and one containing the major part of the heavy particles and the other the major part of the light particles.

The fractions produced by the centrifugal separation may be subjected to subsequent separating treatments to separate the mineral particles from those of the parting liquid and such operations may be efiected by screening in successive stages, for example, two. In the first screening stage, the mineral particles are separated from undiluted parting liquid while, in the second stage, the fraction undergoing treatment is washed and dilutedparting liquid results.

Instead of being screened, one or both fractions produced by the centrifugal separation may be classified in another centrifugal separator and, when the fractions are thus treated, it will be necessary to add water thereto. In the case of the lightfraction, the addition of water is necessary, because the difference in specific gravity between the light particles of the mineral material and the parting liquid is not sumciently great to permit a good separation to be made. In the case of the heavy fraction, the material leaves the main centrifugal separator in the form of a thick slurry and water must be added thereto to permit centrifugal treatment thereof.

The undiluted parting liquid obtained by treatment of either or both of the fractions may be utilized in whole or in part by returning it for addition to the parting liquid that is to be mixed with the mineral material to produce the mixture to be fed to the centrifugal separator. The diluted parting liquid may similarly be utilized in whole or in part. Thus, after partial de-watering, it may be added to the parting liquid to be used for producing the mixture with the mineral materials, or it may be utilized without de-watering to lower the specific gravity of parting liquid, which has been subjected to a preliminary separation in which its water content has been reduced more than is suitable for its use in a separation operation according to the float and sink principle.

The fractions of the mineral material produced by the centrifugal separation may be further treated by means of a hydro-separator with slmultaneous addition of water or, after the addition of water, they may be subjected to magnetic separation, in the event'that the parting liquid is an aqueous suspension of magnetic iron ore. The fractions may also be subjected to flotation after the addition of water thereto, and two or more of the methods mentioned may be used, if desired.

Ordinarily in the practice of the method of the invention, the separation of the mineral material into two fractions may be satisfactorily performed in a single centrifuging operation, but, if desired, the separation may be carried out in successive centrifuging steps. When a stage operation is used, the specific gravity of the material being treated will be lowered by successive additions of water between successive stages.

The practice of the invention may be better understood by reference to the accompanying drawing;in which the single figure is a flow sheet.

Referring to the drawing, the mineral material which has been reduced as above described is shown as being subjected to an initial separation to remove both oversize and undersize particles. For this purpose, the material is fed to a vibrating screen ID, by the action of which the coarse particles are removed and discharged as indicated by the arrow II. The material that has passed through the screen is fed to a second vibrating screen i2 through which the undersized particles are discharged as indicated by the arrow II. The screen material is then conveyed to a mixing tank I, where it is mixed with parting liquid.

The parting liquid, consisting of an aqueous suspension of finely ground material, is shown as being given a preliminary treatment in a centrifugal separator I5 for the elimination of oversized particles and partial de-watering. The coarse material leaves the separator as indicated -by the arrow it and the partially de-watered parting liquid is then fed into the mixing tank ll.

Recovered undiluted parting liquid is also fed into the tank as indicated by the line I! and recovered. diluted liquid is supplied to the tank as indicated by the line it. The mineral material has preferably been wet ground, so that it contains some water, and the de-watering of the parting liquid in the separator 15 is so carried on that the addition of water from the ground material and the use of a selected amount of diluted parting liquid will result in the parting liquid in the mixing tank having the desired specific gravity.

The mixture produced in the mixing tank is fed into a centrifugal separator is from which two fractions are discharged, as indicated at 20, 2 I. Both fractions contain parting liquid and the fraction discharged at 20 contains the major part of the heavy particles, while the fraction discharged at 2i contains the major part of the light particles. Either or both of these fractions may be subjected to a further separating treatment, but, in the flow sheet illustrated, only the light fraction is thus treated. This fraction is first fed to a vibrating screen 22, which produces a separation of the light mineral particles from the undiluted parting liquid and all or a. part of the recovered liquid may be returned to the tank ll.

The mineral particles passing from the top of screen 22 are fed to a screen 23 on which the particles are washed by water sprays 24. The use of the wash water causes diluted parting liquid to be separated from the mineral particles and all or part of the diluted parting liquid may be returned to the tank I. The mineral particles passing off the top of screen 23 are then delivered to a discharge point 25 and constitute one of the be subjected to centrifugal separation as above described, and, when the mineral material is preliminarily subjected to centrifugal separation,

prior to the main separation, the subsequent treatment of the light fraction can ordinarily be carried out satisfactorily only by centrifugal action and with the addition of a large amount of water.

In the practice of the new method in the treatment of coal of a relatively high ash content of from 15 to 20 per cent, it has been found that an excellent separation is obtained, the ash content being reduced to 2 to 3 per cent. In addition, there is a substantial yield of inflammable substance from the separated material. Such results were obtained in an operation in which about 20 to 25 tons of raw coal were treated per hour in a centrifugal separator with a diameter of approximately 800 mm. When a separator havinga diameter of about 1500 mm. is employed, about 40 to 50 tons of raw coal per hour may be handled.

. For the purpose of comparison, coal of the kind separated in the operations above referred to was subjected to separation in an operation involving the use of the sink and float principle and with the separation effected wholly by gravity. It was found that the product obtained was less pure than that obtained by the practice of the new method, in that the ash content was not so greatly reduced, and also the recovery of inflammable material was not as good. Coal of the same type was also subjected to separation by flotation and it was found impossible to obtain a concentrate with an ash content of less than 5 to 10 per cent, if a reasonable recovery was obtained.

What I claim is:

A method of separating a mineral material containing components of different specific gravities into fractions made up mainly of light and heavy particles, respectively, which comprises preparing a parting liquid by forming an aqueous suspension of at least one finely round substance, subjecting the parting liquid to centrifugal separation to remove oversize barticles and reduce the water content, mixing the ground material to be treated with the parting liquid, separating the mixture by centrifugal action into two fractions, each containing some of the parting liquid and one containing the major part of the light particles and the other the major part of the heavy particles, separating the particles in at least one of the fractions from the parting liquid contained therein to recover undiluted parting liquid, washing the separated particles to recover diluted parting liquid therefrom, and adding to the parting liquid of reduced water content at least a portion of the recovered undiluted parting liquid and so much of the recovered diluted parting liquid as is necessary to produce a parting liquid therein.

JQRGEN OLAV CLEEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,909,159 Ashmead May 16, 1933 2,109,234 Keenan Feb. 22, 1938 2,135,957 Wuensch Nov. 8, 1938 2,190,637 Rakowsky Feb. 13, 1940 2,271,501 Scott Jan. 27, 1942 FOREIGN PATENTS Number Country Date 162,591 Spain Aug. 16, 1943 115,681 Sweden Jan. 22, 1946 

